In aggregate material washing machinery, aggregate materials are typically passed through a rotating cylindrical drum and mixed with wash water or cleaning fluid. Generally, the cylindrical drum incorporates interior agitator elements that tumble the aggregate through the wash water as the drum rotates. After the aggregate is scrubbed in wash water it is transferred to a chute or conveyor.
While apparatus provided heretofore were generally somewhat satisfactory for the purpose intended, periodic maintenance is required. For example, typically the agitator elements on the interior of the drum become fouled and deteriorate during use and have to be periodically cleaned or replaced. This requires emptying the drum of aggregate and wash water and then cleaning or replacing each agitator element. Since each element is often bolted to the interior, the procedure is inconvenient and adds to the downtime of the apparatus.
As another disadvantage of the prior art, during operation wash water tends to accumulate in the interior of the drum. Even though the drum rotates, some of the water, particularly at the water surface, is not agitated by the internal elements of the drum. This is so because the agitator elements cut through the wash only at the inner wall of the drum; the surface of the wash not being sufficiently agitated thereby. The wash water becomes stagnate and loaded with silt reducing the cleaning efficiency. The water occasionally freezes during cold weather especially during overnight shut-down periods.
Thus, in the prior art, to prevent stagnation and/or freeze-up, the drum must be periodically drained especially at the end of the day during freezing weather. In the past, one proposal to alleviate the problem has been to provide spaced apertures in an end wall to continuously drain water during aggregate washing. However, the end wall apertures are undesirable insofar as they tend to drain excessive water at the start of a run, and then become clogged toward the end of the run. In freezing weather, the overnight residue invariably freezes around the apertures. The sediment in the water is not positively removed and thus prevents the efficient cleaning, and it must be manually removed the next day by a special maintenance crew. Also, the apertures weaken the end wall structure.
In the prior art, a cylindrical screen is sometimes provided at the outlet of the drum for simultaneously draining and transferring the aggregate to the output chute or conveyor. It often occurs that particles of aggregate become jammed in the screen and prevent efficient draining. Periodically, the apparatus has to be shut down for cleaning the screen further adding to downtime.